That's because bicycles dissolve in water. It is a fundamental limitation of bicycle physics that cannot be solved.

Mine personally combusts into a giant ball of flames if I hit a small puddle. It's really annoying going through so many fire extinguishers.

In actuality I've driven my jank as fuck ebike in torrential rain without a problem. This is with an external battery I slapped on and wired in parallel with the integrated battery. The connectors are sealed by electrical tape alone and it's been perfectly fine for two years. Water is a non-issue of all the important stuff is integrated and sealed correctly.